TEIF: Behind the scenes

cthia wrote:And you are absolutely certain of that because of first hand experience? It is simple physics, you don't have to be in the blast zone to experience the effects if a powerful vacuum. Depending on the wind, time, and the location of the victims, the gaseous cloud may not penetrate the area. The bomb does have a limit. Being on the borderline may save you from the full blast effect, but it does not necessarily save you from the vacuum effect. Bomb effects usually color outside the lines. This forum has always had a problem with what occurs on paper as opposed to what occurs in real life.

The reason it is called a "vacuum bomb" is due to the negative pressure phase of the shock wave. I have included a picture from the Economist that shows the blast pressure wave from regular high-explosive and an air-fuel explosion. The regular high explosive blast is more localized; whereas the spread of the fuel gives a lower peak force, but a broader and more sustained wave.

PS: Are you saying that you do have "first hand experience"?
Shock Wave Pressure

cthia wrote:It is simple physics, you don't have to be in the blast zone to experience the effects if a powerful vacuum. Depending on the wind, time, and the location of the victims, the gaseous cloud may not penetrate the area. The bomb does have a limit. Being on the borderline may save you from the full blast effect, but it does not necessarily save you from the vacuum effect. Bomb effects usually color outside the lines. This forum has always had a problem with what occurs on paper as opposed to what occurs in real life.

But with a Thermobaric explosion (or any kind of explosion) you're only in the "vacuum effect" area (not a hard vacuum, simply an area of below standard atmospheric pressure) if you'd already experienced the overpressure blast wave.

The vacuum is caused by the momentum of the heated air molecules involved in the blast and overpressure wave -- the explosion accelerates them to high speed and they continue outward, creating overpressure, and transferring that outward momentum to other air particles they run into. Their momentum is such that once they finally come to a stop the area behind them -- closer to the point of explosion -- has fewer air molecules per square meter than the wider surrounding air (because so many have been shoved away by the blast). And of course all the air molecules involved have been cooling since the explosion further reducing the pressure. And so with the surrounding atmospheric pressure now somewhat higher than the pressure near the blast point the wind reverses direction and rushes back towards the point of explosion to try to equalize the pressures.

But that low pressure area is pretty transient -- only long enough for the blast wave to exhaust itself, over expand, and collapse back in. We're talking a handful of seconds since the explosion -- and humans can survive exposure complete vacuum for that long without significant injury. (And of course to closer you are to the point where the pressure wave finished over expanding and revered the smaller the pressure difference behind it is -- so if you're far enough away that the overpressure didn't get you the underpressure's not going to either)

Jonathan_S wrote:But that low pressure area is pretty transient -- only long enough for the blast wave to exhaust itself, over expand, and collapse back in. We're talking a handful of seconds since the explosion -- and humans can survive exposure complete vacuum for that long without significant injury. (And of course to closer you are to the point where the pressure wave finished over expanding and revered the smaller the pressure difference behind it is -- so if you're far enough away that the overpressure didn't get you the underpressure's not going to either)

One possible imbalance is if the human body is more resistant to an over-pressure than an under-pressure; then there can be a critical distance where the initial over-pressure is just survivable, but the following under-pressure is fatal. Also the quick switch from over to under pressure can have an effect. However these pressure waves are both part of the blast shock wave, so there is no action at a distance; if is just a question of which part of the blast wave kills you.

The history of these explosions goes back to WW1, but it was only during and after WW2 that their development and use accelerated. The Wikipedia article concludes with this statement:

International law does not prohibit the use of thermobaric munitions, fuel-air explosive devices, or vacuum bombs against military targets. Their use against civilian populations may be banned by the United Nations (UN) Convention on Certain Conventional Weapons (CCW). As of February 2022, all past attempts to regulate or restrict thermobaric weapons have failed.

tlb wrote:

Jonathan_S wrote:But that low pressure area is pretty transient -- only long enough for the blast wave to exhaust itself, over expand, and collapse back in. We're talking a handful of seconds since the explosion -- and humans can survive exposure complete vacuum for that long without significant injury. (And of course to closer you are to the point where the pressure wave finished over expanding and revered the smaller the pressure difference behind it is -- so if you're far enough away that the overpressure didn't get you the underpressure's not going to either)

One possible imbalance is if the human body is more resistant to an over-pressure than an under-pressure; then there can be a critical distance where the initial over-pressure is just survivable, but the following under-pressure is fatal. Also the quick switch from over to under pressure can have an effect. However these pressure waves are both part of the blast shock wave, so there is no action at a distance; if is just a question of which part of the blast wave kills you.

I don't think the human body is all that vulnerable to underpressure. The top of Everest is 1/3rd standard pressure, so around 4.9 PSI, and while you need supplemental oxygen to stay up there for long the pressure in and of itself isn't a problem. And NASA uses 4.3 PSI for space suits (again at high oxygen concentrations) and originally planned to do about the same for the Apollo missions -- so they weren't worried about astronauts spending most of a week at below 1/3rd standard pressure.

Now a few minutes at 1 PSI will kill you, even with supplemental oxygen - that's the Armstrong limit where the exposed liquid in your saliva, tears, urine, and within your lungs will boil at body temperature. But even at that pressure you can survive some seconds with nothing but a weird feeing of your saliva boiling on your tongue. And a thermobaric is creating no more than a few seconds of low pressure -- and I seriously doubt it's as low as 1 PSI anyway.

Jonathan_S wrote:I don't think the human body is all that vulnerable to underpressure. The top of Everest is 1/3rd standard pressure, so around 4.9 PSI, and while you need supplemental oxygen to stay up there for long the pressure in and of itself isn't a problem. And NASA uses 4.3 PSI for space suits (again at high oxygen concentrations) and originally planned to do about the same for the Apollo missions -- so they weren't worried about astronauts spending most of a week at below 1/3rd standard pressure.

Now a few minutes at 1 PSI will kill you, even with supplemental oxygen - that's the Armstrong limit where the exposed liquid in your saliva, tears, urine, and within your lungs will boil at body temperature. But even at that pressure you can survive some seconds with nothing but a weird feeing of your saliva boiling on your tongue. And a thermobaric is creating no more than a few seconds of low pressure -- and I seriously doubt it's as low as 1 PSI anyway.

Although I mainly agree with you, Cthia did not invent the scare stories about this weapon. For example, the Economist headlined an article in 9 March 2022 with this sentence:

SINCE RUSSIA invaded Ukraine on February 24th, Ukrainian officials and human-rights organisations have raised the alarm over the possible use of thermobaric weapons or “vacuum bombs”, with horrifying accounts of how they suck the air out of victims’ lungs.

However The Journal of Military and Veterans’ Health from Australia published this article (summary shown):

Thermobaric munitions are those munitions that, by design, produce more heat and overpressure than conventional explosives by exploding a vapour in the blast zone. Their main use initially was in airborne fuel-air explosive bombs. Whilst the United States has concentrated on airborne weapons, Russia has produced thennobaric weapons and warheads, from airborne bombs to rifle grenades.

Their medical effect is principally primary blast and they affect organs where there is a tissue interface of varying densities, such as the lungs, bowel and inner ear. Damage manifests itself in the severity and onset of occurrence, depending on distance from the blast and orientation of the victim, and can be diagnosed by simple investigative techniques.

This paper was originally written as a presentation for the Australian Military Medical Association Annual Conference in October 2001 and was displayed as a poster at the Defence Health Symposium in 2002.

The blast wave effect has been compared to having a baseball bat hit every square inch of your body at the same time.

The low-pressure effect is pretty minor in comparison.

kzt wrote:The blast wave effect has been compared to having a baseball bat hit every square inch of your body at the same time.

The low-pressure effect is pretty minor in comparison.

Now imagine the low pressure effect coming on the heels of the blast wave effect.

kzt wrote:The blast wave effect has been compared to having a baseball bat hit every square inch of your body at the same time.

The low-pressure effect is pretty minor in comparison.

cthia wrote:Now imagine the low pressure effect coming on the heels of the blast wave effect.

It seems to me that is exactly the situation that KZT is talking about: the low immediately follows the high pressure (and is minor in comparison).

cthia wrote:

kzt wrote:The blast wave effect has been compared to having a baseball bat hit every square inch of your body at the same time.

The low-pressure effect is pretty minor in comparison.

Now imagine the low pressure effect coming on the heels of the blast wave effect.

After the few hundred (peak 450) psi overpressure blows by even atmospheric pressure 14.7 psi would feel like a massive low pressure. I'm not sure you could even tell the difference between 14.7 and 5 psi in the wake of getting slammed by that overpressure blast wave.

Jonathan_S wrote:But that low pressure area is pretty transient -- only long enough for the blast wave to exhaust itself, over expand, and collapse back in. We're talking a handful of seconds since the explosion -- and humans can survive exposure complete vacuum for that long without significant injury. (And of course to closer you are to the point where the pressure wave finished over expanding and revered the smaller the pressure difference behind it is -- so if you're far enough away that the overpressure didn't get you the underpressure's not going to either)

Minor disagreement. Humans can survive a short exposure to vacuum without injury, but we can not survive an instant's exposure to vacuum. While the lack of air itself only does meaningful harm from a lack of oxygen the sufficiently sudden loss of the air inflicts lethal lung damage.

From a practical standpoint I would think the only risk from low pressure would be to those inside the zone but not exposed to the blast front. Say, somebody in a hole in the ground. I have never seen information on how big the threat is.